Differential Material? 5

[Timms]

I am trying to get an idea of what material to use if I want to build a differential for a very small vehicle? Does anyone have recommendations? What do most automobiles have?

Blessings

 

[Timms]

Thanks a lot guys! You have all been really helpfull. The A356 T6 sandcast sounds attractive but it's elogation before break is only 3% and it's strength is 20ksi. The differential will take a fair amount of pounding since it is part of the unsprung mass in the suspension rather than the sprung mass. Also, we intend to enlarge the design to fit bigger gears. Do you think the Aluminum will take this kind of pounding? It would be nice to go with the aluminum since it is so light. Originally the design used ductile iron with renforcement straps. Prhaps I should stick with the ductile iron in order to maintane enough strength and ductility. Ductile iron has a much greater yeild and better ductility as far as I can determine.

Blessing to you all!

 

[NickE]

If you need more strength (and it sounds like you do) then you might have to go to an iron casting, this of course will drop cost of material. You might want to try ADI (austempered ductile iron) it was pretty cool stuff another grad student was working on when I was doing my Ms on Grey iron.

Try here for more info on ADI:

http://www.castsolutions.com/WebsiteOnly/0503/WebOnly0503.pdf

google it for tons of links (including foundries that can cast it up for you)

 

[GregLocock]

We've got at least half a million cast iron diffs on beam axles out there. I think you can be happy that they are strong enough.

I really doubt that aluminium would not be up to the job, but you would have to design it. I mean, we are engineers, right?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Timms]

Thanks alot guys!

Yeah, I think I would like to design an aluminum differential, but I will have to see how soon my boss wants the first prototype ready. I have a few other major tasks to complete first before I can start redesigning a differential.

You guys have been a great help! I hope one day I can return the favour.

Blessings!

 

[thundair]

Let me chime in again with a plug for rapid fab or the trademark name of 'Quick Cast" this is done with SLA which is your pattern made from a 3D data base. Check with John List

http://www.protocastjlc.com/

in Conoga Park he can tell you how many parts he can run, with that pattern.

Check with Gary Vassighi at 3DCam

http://www.3d-cam.com/

for help with the stereolithography pattern.

One other point is I have made housings out of welded 6061 and treated to T6 and it was a miserable twisted piese of crap. If I did it again I would jig weld it and leave plenty of room for post machining.

Also when you talk to John List he can help you with alum material that is stronger than 356 T6.


Regards

 

[thundair]

One last thing ansd I will let this rest...

I worked at a place that made turbine blades and they were forged ...

That being said I wouldn't dismiss any option even forging without a cost inquery.

I once had a manager at Rocketdyne tell me that cnc was to expensive..and my point is look at evrything even forgings..
NickE will tell you that its strength is it the grain direction.

Regards

 

[Timms]

thundair

Thanks for the heads up. I have sent an email to John List. Hopefully he can help.

Blessings

 

[eddyesi]

I have seen a few SAE papers on this that may be of use if you have access to them, based around the design of housings for Formula SAE torsen differnetials. May be of use as these are bike engined single seat cars, so will use a very similar chain driven differential rear axle

 

[Tmoose]

Part geometry and material must be part of the design to be successful.

here is a production rear axle housing apparently fabbed as weldment. The diff proper is still a ferrous casting of some sort.

http://www.4x4wire.com/toyota/reviews/rockplate/05.jpg

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Keeping bearing bores/seats to size in aluminum and even Stainless steel housings is a painful process, frought with unhappy compromises. British motorcycles using aluminum connecting rods with insert type bearings develop negative clearances in real cold weather. Not that I'd expect one to start or run in those circumstances.